In gas-operated devices, it is frequently required to utilize valves that are electrically opened and reliably close in the currentless state. In order to achieve the desired protection against malfunctions of valve components, two valves are usually arranged one behind another in the gas flow, with the two valves opening and closing independently of one another. If one of the valves becomes stuck in the open position, the second valve is still able to close and shut off the valve assembly, i.e., it is ensured that the valve assembly is closed.
There also exists double-seat valve assemblies, in which both valves and the corresponding solenoid actuators are structurally combined with one another. For example, EP 0 757 200 B1 discloses a double-seat valve of this type with two coaxial valve seats that are axially spaced apart from one another, with a separate valve closing element being assigned to each valve seat. The two independent valve closing elements are opened by means of a solenoid actuator with a single magnetizing coil and an external magnetic circuit. Associated with this circuit are two armatures, one armature being realized in a hollow-cylindrical manner (with a closed upper end), and the other armature being realized in the form of a cylinder. The two armatures are arranged coaxial to one another such that the cylindrical armature is situated in the hollow-cylindrical armature.
During a magnetic excitation of the magnetic circuit, a part of the flux line extends through the outer armature and the other part of the flux line extends through the inner armature such that both armatures are attracted and both valve closing elements are moved into the open position. However, dimensions are somewhat critical to this arrangement since it must be assured that the inner armature receives sufficient magnetic flux. This requires a relatively intense magnetic excitation of the magnetic circuit, and correspondingly dimensioned coils and control circuits.
EP 1 084 357 B1 discloses a double-seat valve assembly in which the integration or combination of both valves is even more advanced. A common valve seat is associated with both valve closing elements. The valve closing elements are arranged concentric to one another. In this case, only the inner valve closing element is connected to an armature and the outer valve closing element is connected to a non-magnetic sleeve that surrounds the armature.
Although this arrangement makes it possible to easily control two valve closing elements with a single coil, it causes a relatively high leakage flux because the non-magnetic sleeve completely surrounds the inner armature.
The electrical control of solenoid valves is a significant cost factor. In this respect, one attempt to realize the assembly with the smallest coils possible, i.e., with the lowest quantities of copper and with low control currents, particularly with low holding currents. On the other hand, it must be ensured that the valve closes when the current is switched off or an outage occurs.
Based on these circumstances, the invention aims to develop a simply designed and reliable solenoid valve assembly that can be controlled with low currents.